1. Field of the Invention
The present invention relates to a camera having a movable unit of, e.g., a lens moved to a target position according to a drive operation of a motor, and, more particularly, to a camera moving amount control apparatus for precisely stopping a movable unit at a target position.
2. Description of the Related Art
For an auto-focusing apparatus as a moving amount control apparatus for driving a photographing lens and stopping it at an in-focus position, a method proposed in, e.g., Published Unexamined Japanese Patent Application No. 63-153526 is known. In this method, information representing an optimal deceleration curve of the photographing lens is stored in a storage means, a moving speed of the photographing lens is detected by a detection means, and the detected moving speed is sequentially compared with the information representing the deceleration curve stored in the storage means, thereby turning on/off or braking a motor to control an acceleration/deceleration operation. With these operations, the photographing lens is decelerated to the in-focus position along the deceleration curve, and is precisely stopped at a target position.
However, when the deceleration control of the photographing lens is performed by this method, the motor must be turned on to accelerate the photographing lens when the photographing lens comes close to the infocus position. In this case, the photographing lens tends to overshoot the target position. In order to avoid such a state, the above-mentioned auto-focusing apparatus employs a limited acceleration method for limiting an ON time of the motor.
Some film auto wind-up devices perform control using a deceleration curve like in the above-mentioned apparatus, as proposed in, e.g., Japanese Patent Application No. 63-027903 (corresponding to U.S. Pat. No. 4,878,077). In this case, the device also has a means for limiting an ON time of a motor according to a signal from a speed detection means near a target position, and the means is operated to prevent an overacceleration state.
The deceleration control using a deceleration curve is very effective as a method of precisely stopping a movable unit of, e.g., a photographing lens, a film, or the like. Acceleration attained by turning on a motor and deceleration attained by braking the motor are appropriately repeated to realize a speed along the deceleration curve. However, when the motor is turned to accelerate the movable unit near a stop position like in normal control, an overacceleration state tends to occur. A special means for, e.g., switching control to prevent the overacceleration state near the stop position must be taken, resulting in complicated control.